1. Technical Field of the Invention
The present invention relates generally to an apparatus and method for providing hypothermic brain preservation in instances where pulmonary or cardiac dysfunction has occurred.
2. Description of the Related Art
The human body requires oxygen in order to sustain itself. The heart and lungs provide means for providing the oxygen to the other parts of the body. They work together to supply body tissues with life giving oxygen. Air, the body's source of oxygen, is carried to the lungs by breathing. Oxygen in the inhaled air is absorbed into the blood and then pumped to the heart by means of the circulatory system. The circulatory system has a double loop since initially blood is pumped from two chambers of the four chambered heart via the pulmonary artery to a network of capillaries in the lungs which enrich the blood with oxygen. The oxygen rich blood then travels back to the heart via the pulmonary vein to the two other chambers of the four chambered heart whereupon the oxygenated blood is pumped from the heart ventricle via the aorta to networks of capillaries to transfer oxygen to the body tissues and organs. After travelling through the network of capillaries that form the circulatory system connected to tissues and organs, the oxygen depleted blood travels back to the heart via the vena cavae. The process is then repeated. The keystone to the circulation is the heart. Without the heart pumping, the blood will not circulate, and the tissues and organs that require oxygen will cease to function. A particularly vital recipient of the oxygenated blood supply is the brain. The brain receives 25% or more of the body circulation of cardiac output. If a person has suffered a cardiac arrest and as a result, has experienced a cessation of heartbeat and cardiac function, there is a limited amount time to rectify the situation before irreversible damage occurs, especially in the brain. The brain is particularly sensitive to oxygen. In certain situations when the lungs are deprived of oxygen, the blood does not get oxygenated, and the brain is deprived of oxygen. Again in this situation, reversible and irreversible brain damage occurs.
In recent years, the medical profession has developed emergency resuscitation techniques performed at the scene of a cardiopulmonary event. At this time the lungs and/or heart are failing and the resuscitative procedures are performed. Some cardiac action almost invariably persists and when this cardiac action is not present a rhythmic compression of the heart and chest is performed to maintain circulation. This procedure is known as cardiopulmonary resuscitation (CPR). The technique is used to start the heart pumping and to restore the flow of oxygen rich blood. When this action commences timely, the person can survive the episode.
The presence of permanent brain damage, as more specifically set forth below, is the point of no return during cardiopulmonary resuscitation.
If the brain is starved of oxygen, brain damage spreads throughout the cortex or surface areas of the brain. As a result, a decorticate condition develops eliminating motor and sensory functions and leaving the central brain and brain stem to function at a very basic level maintaining a basal heart rate and basal respiratory drive. In CPR, the clinical presence of fixed dilated pupils (FDP) identifies the loss of a very protective reflex. Fixed dilated pupils do not respond to external stimuli such as light, that is, the pupils are fixed. For many years, FDP have been used clinically to guide physicians and health care personnel in making medical decisions as to the state of the health of the patient. In most instances, the finding of FDP gives rise to an inference of or confirms the presence of brain damage. The finding of FDP along with absent peripheral pulses and no evidence of a beating heart may lead to the suspension of efforts and an acceptance of death. Irrevocable treatment decisions must be made in a few seconds and the determination and its consequences may result in irreversible brain damage.
There are instances in which individuals who displayed FDP were successfully resuscitated. A variety of CPR methods were used depending upon the cause of cardiac or pulmonary failure. In successful CPR, external massage has been associated with the return of the pupillary light reflex during rhythmic chest and cardiac compression. If the benefit or efficiency of CPR is lost, FDP returns. The pupils are in the clinical setting, an effective monitor of the efficiency of CPR Clinical experience in the field has repeatedly demonstrated that fixed dilated pupils do not necessarily indicate that permanent brain damage is present. Some medical authorities have concluded that FDP are a grave warning, but are not necessarily an irrevocable indicator of the point of no return.
There have been a number of clinical situations wherein the hypothermic state, with its abnormally low temperature, has been associated with FDP and no trace of radial artery and femoral artery pulses only to find a slowly beating heart and a palpable carotid pulse. The brain is more susceptible to reversible and subsequently irreversible damage than the heart and lungs. Therefore, the brain usually suffers irreversible damage before the heart and lungs become irretrievable.
However, numerous anecdotal reports of successful hypothermic resuscitations using traditional techniques have been followed by memory loss or other subtle indications of brain damage. On the other hand, hypothermic anesthesia techniques to levels of 15.degree. C. create a window of one hour or more for elective brain surgery. These hypothermia techniques clearly protect brain function.
In 1991, researchers developed partial liquid ventilation (PLV). In this procedure, the lungs are partially filled with perfluorocarbons while the remaining portion of the pulmonary tree are ventilated with fresh oxygen which is pumped into the remaining open always using a conventional ventilator. In the PLV procedure, perfluorocarbons have been utilized in the lungs in situations where oxygen was carried to the pulmonary tree by dissolving the oxygen in the perfluorocarbons and ventilating the lungs with oxygen rich perfluorocarbon solution. This procedure differs from the present invention in that the present invention uses a cooled fluid to provide rapid hypothermic brain protection as a part of cardiopulmonary resuscitation when FDP are first noted; whereas the PLV method uses the fluorocarbons in the lungs, but for a totally different purpose. In PLV, the fluid, containing oxygen, aids the air sacs in the lungs which have collapsed.
The proposed method of hypothermic brain preservation (HBP) differs significantly from PLV in that the lungs must be completely filled with a friendly fluid, not necessarily perfluorocarbons, to induce hypothermia and have brain preservation. In HBP the primary goal is to remove calories from the brain and lower the brains temperature in order to provide a greater period of time during which heart and lung function can be restored by a variety of methods and/or techniques.
Other objects and features as well as additional details of the present invention will become apparent from the following detailed description and annexed drawings of the presently preferred embodiments thereof, when considered in conjunction with the associated drawings.